On Mon, Aug 07, 2006 at 11:47:53PM -0700, Andrew Morton wrote:
> On Mon, 7 Aug 2006 17:55:55 -0500 [email protected] (Linas Vepstas) wrote:
> > The current code in register_chrdev_region() attempts to check
> > for overlapping regions of minor device numbers, but performs
> > that check incorrectly. For example, if a device with minor
> > numbers 128, 129, 130 is registered first, and a device with
> > minor number 3,4,5 is registered later, then the later range
> > is incorrectly identified as "overlapping" (since 130>3),
> > when clearly this is the wrong conclusion.
> >
> > This patch fixes the overlap check to work correctly.
>
> I yesterday merged the below. Do you agree that it will fix the bug?
Hi Andrew. It does fix the original bug, but it introduces the bug that
Linas pointed out. After looking at Linas' fix and finding an
off-by-one error in his code, I decided that we had better have a
stand-alone harness that we can put the various versions of the function
in to verify them without having to reboot a kernel. The harness is
below the patch, with the test results of all five implementations.
Can you please back out my original patch and use this instead? I have
run it through the test harness and I am much more confident in its
correctness. Linas can you take a look at this and make sure you agree?
Signed-off-by: Amos Waterland <[email protected]>
---
char_dev.c | 28 +++++++++++++++++++++++-----
1 file changed, 23 insertions(+), 5 deletions(-)
diff --git a/fs/char_dev.c b/fs/char_dev.c
index 3483d3c..e13157f 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -109,13 +109,31 @@ __register_chrdev_region(unsigned int ma
for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
if ((*cp)->major > major ||
- ((*cp)->major == major && (*cp)->baseminor >= baseminor))
+ ((*cp)->major == major &&
+ (((*cp)->baseminor >= baseminor) ||
+ ((*cp)->baseminor + (*cp)->minorct > baseminor))))
break;
- if (*cp && (*cp)->major == major &&
- (*cp)->baseminor < baseminor + minorct) {
- ret = -EBUSY;
- goto out;
+
+ /* Check for overlapping minor ranges. */
+ if (*cp && (*cp)->major == major) {
+ int old_min = (*cp)->baseminor;
+ int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
+ int new_min = baseminor;
+ int new_max = baseminor + minorct - 1;
+
+ /* New driver overlaps from the left. */
+ if (new_max >= old_min && new_max <= old_max) {
+ ret = -EBUSY;
+ goto out;
+ }
+
+ /* New driver overlaps from the right. */
+ if (new_min <= old_max && new_min >= old_min) {
+ ret = -EBUSY;
+ goto out;
+ }
}
+
cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
---
$ gcc -g -O0 -Wall -Werror test-register.c -o test-register
$ ./test-register
OVERLAPPING MINORS
NAME MIN MAX DRIVER PASS
linus: 0 3 first OK
linus: 1 4 second FAIL
amos: 0 3 first OK
amos: -1 -1 NULL OK
andrew: 0 3 first OK
andrew: -1 -1 NULL OK
linas: 0 3 first OK
linas: -1 -1 NULL OK
amos2: 0 3 first OK
amos2: -1 -1 NULL OK
NON-OVERLAPPING MINORS
NAME MIN MAX DRIVER PASS
linus: 128 130 first OK
linus: 3 5 second OK
amos: 128 130 first OK
amos: -1 -1 NULL FAIL
andrew: 128 130 first OK
andrew: -1 -1 NULL FAIL
linas: 128 130 first OK
linas: 3 5 second OK
amos2: 128 130 first OK
amos2: 3 5 second OK
CORNER CASES
NAME MIN MAX DRIVER PASS
linas: 0 2 first OK
linas: 10 12 second OK
linas: 5 7 third OK
linas: -1 -1 NULL OK
linas: -1 -1 NULL OK
linas: -1 -1 NULL FAIL
linas: 13 13 seventh OK
amos2: 0 2 first OK
amos2: 10 12 second OK
amos2: 5 7 third OK
amos2: -1 -1 NULL OK
amos2: -1 -1 NULL OK
amos2: 9 9 sixth OK
amos2: 13 13 seventh OK
---
/* Released under the GPL. */
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define CHRDEV_MAJOR_HASH_SIZE 255
#define GFP_KERNEL 0
#define ENOMEM 12
#define EBUSY 16
#define MAX_ERRNO 4095
#define SHOULD_PASS 0
#define SHOULD_FAIL 1
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#define IS_ERR_VALUE(x) ((x) >= (unsigned long)-MAX_ERRNO)
struct mutex { int count; } chrdevs_lock;
static struct char_device_struct {
struct char_device_struct *next;
unsigned int major;
unsigned int baseminor;
int minorct;
char name[64];
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
long IS_ERR(const void *ptr) { return IS_ERR_VALUE((unsigned long)ptr); }
static inline void *ERR_PTR(long error) { return (void *) error; }
void *kzalloc(size_t size, int flags) { return calloc(1, size); }
void kfree(const void *p) { return; }
int major_to_index(int index) { return index; }
void inline mutex_lock(struct mutex *lock) { return; }
void inline mutex_unlock(struct mutex *lock) { return; }
static struct char_device_struct *
linus__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
struct char_device_struct *cd, **cp;
int ret = 0;
int i;
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
/* temporary */
if (major == 0) {
for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
if (chrdevs[i] == NULL)
break;
}
if (i == 0) {
ret = -EBUSY;
goto out;
}
major = i;
ret = major;
}
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strncpy(cd->name,name, 64);
i = major_to_index(major);
for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
if ((*cp)->major > major ||
((*cp)->major == major && (*cp)->baseminor >= baseminor))
break;
if (*cp && (*cp)->major == major &&
(*cp)->baseminor < baseminor + minorct) {
ret = -EBUSY;
goto out;
}
cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
return cd;
out:
mutex_unlock(&chrdevs_lock);
kfree(cd);
return ERR_PTR(ret);
}
static struct char_device_struct *
amos__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
struct char_device_struct *cd, **cp;
int ret = 0;
int i;
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
/* temporary */
if (major == 0) {
for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
if (chrdevs[i] == NULL)
break;
}
if (i == 0) {
ret = -EBUSY;
goto out;
}
major = i;
ret = major;
}
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strncpy(cd->name,name, 64);
i = major_to_index(major);
for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
if ((*cp)->major > major ||
((*cp)->major == major &&
(((*cp)->baseminor >= baseminor) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))))
break;
if (*cp && (*cp)->major == major &&
(((*cp)->baseminor < baseminor + minorct) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))) {
ret = -EBUSY;
goto out;
}
cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
return cd;
out:
mutex_unlock(&chrdevs_lock);
kfree(cd);
return ERR_PTR(ret);
}
static struct char_device_struct *
andrew__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
struct char_device_struct *cd, **cp;
int ret = 0;
int i;
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
/* temporary */
if (major == 0) {
for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
if (chrdevs[i] == NULL)
break;
}
if (i == 0) {
ret = -EBUSY;
goto out;
}
major = i;
ret = major;
}
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strncpy(cd->name,name, 64);
i = major_to_index(major);
for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
if ((*cp)->major > major ||
((*cp)->major == major &&
(((*cp)->baseminor >= baseminor) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))))
break;
if (*cp && (*cp)->major == major &&
(((*cp)->baseminor < baseminor + minorct) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))) {
ret = -EBUSY;
goto out;
}
cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
return cd;
out:
mutex_unlock(&chrdevs_lock);
kfree(cd);
return ERR_PTR(ret);
}
static struct char_device_struct *
linas__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
struct char_device_struct *cd, **cp;
int ret = 0;
int i;
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
/* temporary */
if (major == 0) {
for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
if (chrdevs[i] == NULL)
break;
}
if (i == 0) {
ret = -EBUSY;
goto out;
}
major = i;
ret = major;
}
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strncpy(cd->name,name, 64);
i = major_to_index(major);
for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
if ((*cp)->major > major ||
((*cp)->major == major &&
(((*cp)->baseminor >= baseminor) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))))
break;
/* Check for overlap of minor ranges */
if (*cp && (*cp)->major == major &&
((((*cp)->baseminor <= baseminor) &&
((*cp)->baseminor + (*cp)->minorct >= baseminor)) ||
(((*cp)->baseminor >= baseminor) &&
((*cp)->baseminor <= baseminor+minorct)))) {
ret = -EBUSY;
goto out;
}
cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
return cd;
out:
mutex_unlock(&chrdevs_lock);
kfree(cd);
return ERR_PTR(ret);
}
static struct char_device_struct *
amos2__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
struct char_device_struct *cd, **cp;
int ret = 0;
int i;
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
/* temporary */
if (major == 0) {
for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
if (chrdevs[i] == NULL)
break;
}
if (i == 0) {
ret = -EBUSY;
goto out;
}
major = i;
ret = major;
}
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strncpy(cd->name,name, 64);
i = major_to_index(major);
for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
if ((*cp)->major > major ||
((*cp)->major == major &&
(((*cp)->baseminor >= baseminor) ||
((*cp)->baseminor + (*cp)->minorct > baseminor))))
break;
/* Check for overlapping minor ranges. */
if (*cp && (*cp)->major == major) {
int old_min = (*cp)->baseminor;
int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
int new_min = baseminor;
int new_max = baseminor + minorct - 1;
/* New driver overlaps from the left. */
if (new_max >= old_min && new_max <= old_max) {
ret = -EBUSY;
goto out;
}
/* New driver overlaps from the right. */
if (new_min <= old_max && new_min >= old_min) {
ret = -EBUSY;
goto out;
}
}
cd->next = *cp;
*cp = cd;
mutex_unlock(&chrdevs_lock);
return cd;
out:
mutex_unlock(&chrdevs_lock);
kfree(cd);
return ERR_PTR(ret);
}
void clear(struct char_device_struct **chrdevs)
{
int i = 0;
for (i = 0; i < CHRDEV_MAJOR_HASH_SIZE; i++)
chrdevs[i] = 0x0;
}
void dump(const char *prefix, struct char_device_struct *cd, int should_fail)
{
if (IS_ERR(cd)) {
printf("%6s: %6i %6i %7s %6s\n",
prefix, -1, -1, "NULL",
should_fail ? "OK" : "FAIL");
return;
}
printf("%6s: %6i %6i %7s %6s\n",
prefix, cd->baseminor, cd->baseminor + cd->minorct - 1,
cd->name, should_fail ? "FAIL" : "OK");
}
int main(int argc, char *argv[])
{
struct char_device_struct *cd;
/* First we test the case that a driver registers 0-3 and then
* another driver comes along and tries to take 1-4. The second
* driver should be rejected.
*/
{
printf("OVERLAPPING MINORS\n");
printf("%6s %6s %6s %7s %6s\n",
"NAME", "MIN", "MAX", "DRIVER", "PASS");
clear(chrdevs);
cd = linus__register_chrdev_region(1, 0, 4, "first");
dump("linus", cd, SHOULD_PASS);
cd = linus__register_chrdev_region(1, 1, 4, "second");
dump("linus", cd, SHOULD_FAIL);
clear(chrdevs);
cd = amos__register_chrdev_region(1, 0, 4, "first");
dump("amos", cd, SHOULD_PASS);
cd = amos__register_chrdev_region(1, 1, 4, "second");
dump("amos", cd, SHOULD_FAIL);
clear(chrdevs);
cd = andrew__register_chrdev_region(1, 0, 4, "first");
dump("andrew", cd, SHOULD_PASS);
cd = andrew__register_chrdev_region(1, 1, 4, "second");
dump("andrew", cd, SHOULD_FAIL);
clear(chrdevs);
cd = linas__register_chrdev_region(1, 0, 4, "first");
dump("linas", cd, SHOULD_PASS);
cd = linas__register_chrdev_region(1, 1, 4, "second");
dump("linas", cd, SHOULD_FAIL);
clear(chrdevs);
cd = amos2__register_chrdev_region(1, 0, 4, "first");
dump("amos2", cd, SHOULD_PASS);
cd = amos2__register_chrdev_region(1, 1, 4, "second");
dump("amos2", cd, SHOULD_FAIL);
}
/* Now we test the case that a driver registers 128-130 and then
* another driver comes along and asks for 3-5. The second driver
* should NOT be rejected.
*/
{
printf("\nNON-OVERLAPPING MINORS\n");
printf("%6s %6s %6s %7s %6s\n",
"NAME", "MIN", "MAX", "DRIVER", "PASS");
clear(chrdevs);
cd = linus__register_chrdev_region(1, 128, 3, "first");
dump("linus", cd, SHOULD_PASS);
cd = linus__register_chrdev_region(1, 3, 3, "second");
dump("linus", cd, SHOULD_PASS);
clear(chrdevs);
cd = amos__register_chrdev_region(1, 128, 3, "first");
dump("amos", cd, SHOULD_PASS);
cd = amos__register_chrdev_region(1, 3, 3, "second");
dump("amos", cd, SHOULD_PASS);
clear(chrdevs);
cd = andrew__register_chrdev_region(1, 128, 3, "first");
dump("andrew", cd, SHOULD_PASS);
cd = andrew__register_chrdev_region(1, 3, 3, "second");
dump("andrew", cd, SHOULD_PASS);
clear(chrdevs);
cd = linas__register_chrdev_region(1, 128, 3, "first");
dump("linas", cd, SHOULD_PASS);
cd = linas__register_chrdev_region(1, 3, 3, "second");
dump("linas", cd, SHOULD_PASS);
clear(chrdevs);
cd = amos2__register_chrdev_region(1, 128, 3, "first");
dump("amos2", cd, SHOULD_PASS);
cd = amos2__register_chrdev_region(1, 3, 3, "second");
dump("amos2", cd, SHOULD_PASS);
}
/* Since it looks like Linas' patch stacked on Amos' patch, which
* is expressed as linus herein, is the correct solution, let's
* hammer it with a few more corner cases. We find that it has
* a false postive in the (10-12) + (9-9) case, so rewrite the code
* to make it clearer (called amos2 herein), which passes all the
* corner cases we know about.
*/
{
printf("\nCORNER CASES\n");
printf("%6s %6s %6s %7s %6s\n",
"NAME", "MIN", "MAX", "DRIVER", "PASS");
clear(chrdevs);
cd = linas__register_chrdev_region(1, 0, 3, "first");
dump("linas", cd, SHOULD_PASS);
cd = linas__register_chrdev_region(1, 10, 3, "second");
dump("linas", cd, SHOULD_PASS);
cd = linas__register_chrdev_region(1, 5, 3, "third");
dump("linas", cd, SHOULD_PASS);
cd = linas__register_chrdev_region(1, 6, 3, "fourth");
dump("linas", cd, SHOULD_FAIL);
cd = linas__register_chrdev_region(1, 9, 2, "fifth");
dump("linas", cd, SHOULD_FAIL);
cd = linas__register_chrdev_region(1, 9, 1, "sixth");
dump("linas", cd, SHOULD_PASS);
cd = linas__register_chrdev_region(1, 13, 1, "seventh");
dump("linas", cd, SHOULD_PASS);
clear(chrdevs);
cd = amos2__register_chrdev_region(1, 0, 3, "first");
dump("amos2", cd, SHOULD_PASS);
cd = amos2__register_chrdev_region(1, 10, 3, "second");
dump("amos2", cd, SHOULD_PASS);
cd = amos2__register_chrdev_region(1, 5, 3, "third");
dump("amos2", cd, SHOULD_PASS);
cd = amos2__register_chrdev_region(1, 6, 3, "fourth");
dump("amos2", cd, SHOULD_FAIL);
cd = amos2__register_chrdev_region(1, 9, 2, "fifth");
dump("amos2", cd, SHOULD_FAIL);
cd = amos2__register_chrdev_region(1, 9, 1, "sixth");
dump("amos2", cd, SHOULD_PASS);
cd = amos2__register_chrdev_region(1, 13, 1, "seventh");
dump("amos2", cd, SHOULD_PASS);
}
return 0;
}
---
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